1. Field of the Invention
The present invention is directed to a device having a scatter-free light valve comprising a cell having two carrier plates which are arranged in parallel to one another to form a chamber therebetween with the surfaces of the plates facing the chamber being provided with electrically conductive transparent coatings and the chamber receiving a layer of material which can be switched between different optical states.
2. Prior Art
A light valve, which has a pair of carrier plates arranged in parallel to form a chamber for receiving a layer of liquid crystal material with the carrier plate having transparent, electrically conductive coatings, is disclosed in British Pat. No. 1,372,868 which corresponds to German Offenlegungsschrift No. 21 58 563.
In order to prevent the glare of sunlight, various visual aids such as a sun visor have been proposed. However, it would be a considerable improvement for the driver of an automobile if he were able to maintain the field of vision, which he must constantly keep in sight, free of obstructions. Preferably, protection gainst sunlight, which was too intense, was provided by pivotable sun visors or tinted windshields or windscreens and protection against too strong a light, which was being reflected by the rear view mirror, was provided by utilizing a tiltable mirror holder. All of these measures are unsatisfactory insomuch as they do not afford an automatic screening and are effective solely in the case of really disturbing light.
While it has already been suggested to carry out an attenuation of the light on a liquid crystal base as disclosed in German Auslegeschrift No. 22 46 415 and in the French published patent application No. 22 28 234. The aforementioned publications do not discuss the mode of the operation of the liquid crystal, which was being used, in detail but obviously a liquid crystal light valve of a dynamic scattering type was intended. However, above a specific threshold voltage, i.e. when the specific light intensity exceeds a given maximum, a dynamic scattering liquid crystal substance develops a milky cloudiness and in this state will not only prevent the high intensity light, but will also block other images from the operator's view.